1. Field of the Invention
The present invention relates to a cleaning device, a process cartridge, and an image forming apparatus, and more particularly to a cleaning device that is capable of efficient cleaning, a process cartridge that incorporates the cleaning device, and an image forming apparatus that incorporates the cleaning device or the process cartridge including the cleaning device.
2. Discussion of the Background
A related-art image forming apparatus, such as a copying machine, a facsimile machine, a printer, or a multifunction printer having two or more of copying, printing, scanning, and facsimile functions, forms a toner image on a recording medium (e.g., a sheet) using an electrophotographic method. In such an image forming apparatus, for example, a surface of a photoconductor, that is a image carrier, is charged by providing a charge with a predetermined polarity. The charged surface of a photoconductor is exposed by a light beam to form an electrostatic latent image. Charged toner of the same polarity as a charging electrode is supplied to the electrostatic latent image to form a toner image on the photoconductor. The toner image formed on the photoconductor is transferred onto a recording medium such as a sheet of paper. The toner image is then fixed onto the recording medium by heat and pressure.
Residual toner that is not transferred during a transfer process of the toner image remains on the surface of the photoconductor. Accordingly, it is necessary to clean the surface of the photoconductor by removing the residual toner before the following charging process. This cleaning is done using a cleaning unit, configured for example, as a cleaning blade and cleaning brush.
A problem arises, however, when downsized toner or spherical toner is used, because it is difficult to remove the residual toner sufficiently using the usual cleaning methods. Therefore, to improve cleaning efficiency, it is proposed to form a thin coating film by applying a lubricant of, for example, fatty acid metal salt, onto the surface of the photoconductor to reduce friction coefficient of the surface of the photoconductor. When the friction coefficient of the surface of the photoconductor is reduced, adhesive force between the toner and the photoconductor decreases and blade cleaning becomes effective, helping to reduce toner filming.
Generally, the lubricant is applied onto the image carrier using a lubricant coating roller, in which a solid lubricant is pressed against the coating roller, such as a brush roller, to shave the lubricant off. The lubricant shaved off by rotating a coating roller is coated on the surface of the photoconductor.
In a cleaning device that includes such a lubricant coating device, whenever a new photoconductor and cleaning blade are installed or it is necessary to print an image at very high resolution the cleaning device is generally operated in a lubricant coating mode, in which the amount of lubricant is deliberately increased. Although such an increase is needed for new parts, if the coating amount of the lubricant is increased during ordinary printing, excess lubricant may attach to the charging roller, possibly resulting in production of an abnormal image and scumming when excess lubricant enters a developing device. Therefore, it is preferable to increase the coating amount of the lubricant only while the device is operating in the lubricant coating mode.
Accordingly, a variety of lubricant coating devices and methods have been employed to implement the lubricant coating mode. For example, the coating mode may include a blind rotation mode between printing operations, in which the photoconductor and the coating roller are rotated without performing an actual printing operation. The blind rotation mode is continued until a sufficient amount of lubricant coats the surface of the photoconductor.
This reliable procedure is highly effective in preventing a blade from being rolled when a new blade is installed and avoiding cleaning failure during printing of an image with high resolution. However, this procedure requires a waiting time because it is not possible to print while the blind rotation mode is performed. Further, the blind rotation mode itself adds wear on sliding members such as roller bearings of the photoconductor and the coating roller the longer it continues, adversely affecting service life of the device.